Study On Drying Properties And Physiochemical Quality Of Superheated Steam In Maize

Maize is one of the major planting crops in China,freshly harvested maize is generally higher water content, large grain,dense skin structure, water loss difficulties, need timely dried to remove moisture in order to achieve the safe storage requirements。At present, China’s maize dried by natural drying and hot air drying,there is overall mechanization level is not high, high energy consumption and with farmers drying reduced, every year a lot of maize due to failure to timely drying and mildew, resulting in a waste of resources. Development of high efficiency drying technology is an effective way to solve the problem of drying maize.In order to investigate the efficient energy-saving grain drying technology, this study attempts to superheated steam drying of maize,studying the characteristics of mazie superheated steam drying,comparative study maize stress- crack index, extrusion crushing force, drying quality forms regulation in different drying process by superheated steam drying and hot air drying, the main conclusions are as follows:(1)Using superheated steam drying technology for drying maize,Explore the impact of the steam temperature, velocity, initial moisture content of the drying characteristics. The results show, the superheated steam drying process has preheating stage and decelerating dry stage, no obvious constant rate drying stage. The preheating stage has the phenomenon of steam condensation, improve the steam temperature and velocity helps to reduce the amount of steam condensation. Drying stage velocity, steam temperature and initial moisture content of maize increase can improve the drying rate. The inversion point is a variable, and it decreases with the increase of the velocity and reduce the initial moisture content of maize. Thin layer drying models for simulating maize drying data and getting dry single diffusion equation,the experimental value and the predicted average relative error is lesser, test results show that the diffusion model can better simulate maize superheated steam drying process.(2)Respectively with hot air and superheated steam as drying medium,comparative study stress- crack index and forms,extrusion crushing force regulation of maize in different drying temperature,velocity and tempering temperature. The results show, with the increase of drying temperature, stress- crack index of maize under the hot air drying and superheated steam drying conditions showed decreased first and then increased trend, in the 150℃stresscrack index is low; with the increase of velocity, stress- crack index has generally upward trend; at 50℃tempering temperature conditions and the crack rate is low. Under the same experimental conditions, the stress- crack index of maize by superheated steam drying is lower than the hot air drying and with a better crack form. Under the two drying methods, maize resistance to extrusion pressure decreases with the increase of temperature; velocity of hot-air dried maize resistant to resistance to extrusion pressure has little effect, superheated steam drying maize resistance to extrusion pressure decreases with the increase of velocity; high tempering temperature increase of superheated steam drying maize grain resisting extrusion pressure. Superheated steam drying of maize grain heat damage is larger and hard in maize grain surface form a hard shell, under the same conditions, the superheated steam drying maize resistant extrusion pressure lower than hot air drying.(3)Comparative study of hot air drying and superheated steam drying maize quality found that the correlation was significant between drying temperature and quality index, With the increase of drying temperature, The brightness of maize powder decreased, and the red degree increased, the starch yield of maize decreased, increase the degree of starch gelatinization,lower free fatty acid value, The effect of superheated steam drying on the degree of maize powder color and starch gelatinization was higher than hot air drying. The increase of velocity, increased the gelatinization degree of maize, the brightness of maize powder decreased, and the red degree increased, the starch yield of maize decreased, free fatty acid value decreased. tempering temperature has little effect on the quality of maize.(4)The drying time, stress- crack index,maize flour color as the evaluation index, superheated steam temperature, velocity and tempering temperature as factors,Through orthogonal experiments, the comprehensive weighted average method is used to optimize the drying process, the drying temperature 150 ℃, velocity of 3 m/s, 50℃tempering temperature, drying effect is better, stress- crack index was 9%, maize stress- crack index is smaller, the drying time was 14 min, The brightness of maize powder is 80.65.